The present invention relates to a pattern forming process, particularly one by lithography for fine fabrication, and also to a thin-film magnetic head formed by said process.
It is a common process of forming a desired pattern on a substrate to coat the substrate with a resist film in conformity with the pattern and then remove the uncoated part of the substrate by means of ion milling. This process is essential for the fine fabrication of those materials which are unsuitable for wet etching or reactive dry etching. The resist used for this process includes, for example, phenol novolak resist, AZ-1350J, made by Shiplay Company. The resist film is formed by the spin coating method which involves the steps of dropping a resist solution of proper viscosity onto a rotating substrate, thereby causing an excess of the resist solution to be driven out by centrifugal force, and drying the remaining resist solution.
The spin coating method, however, does not provide a uniform coating on a substrate having a stepped surface. This is a problem in the production of highly integrated circuits containing multilayered elements and conductors and also in the ever-expanding application areas of thin-film technology. A solution to this problem is the dual layer resist method. This method is applied to the patterning of a substrate 1 having a stepped surface as shown in FIG. 2a. According to this method, at first, a thick resist coating 2 is formed on a substrate 1, and it is flattened. (The resist coating is simply referred to as resist hereinafter.) Then, a second resist 3 is formed on said thick resist 2. Said second resist 3 undergoes exposure and development to form a resist pattern 3a. Using this resist pattern 3a as a mask, the first resist 2 undergoes reactive ion etching by oxygen plasma, so that the resist pattern 2a is formed as shown in FIG. 2c. Using the resist pattern 2a as a mask, the substrate 1 undergoes etching. Thus, the etching Ia of the substrate is performed as shown in FIG. 2d. Incidentally, the dual layer resist method is disclosed in "Dual Layer Resist Material Used for Pattern Transfer by RIE", by E. Reihimanis, G. Smolinsky, and C. W. Wilkins, Jr., Solid Stage Technology (Japanese Version), 1985, 10, pp. 52-57.
The above-mentioned dual layer method poses a serious problem in the case where the pattern is formed by dry etching method, especially physical sputtering method. This problem arises from the fact that the resist pattern formed by the dual layer method has a large thickness, especially in the hollow part of the substrate, and also has nearly vertical etched walls. The deep vertical etched walls cause the particles ejected from the substrate by physical sputtering (such as ion milling and reactive ion etching) to redeposit on them. The redeposited particles, which are indicated by 1a in in FIG. 2d cause dimensional errors or erroneous cross section to the pattern.